Task 2 Briefing

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Information & Communications TechnologyInformation & Communications TechnologyHD in Telecommunications and NetworkingHD in Telecommunications and Networking

Task 2 Briefing

The Design of a

Computer Controlled

Stop Watch

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The Technology Used

Based on the Microcontroller card you have built

Controlled by a C program compiled on PC to run on the Microcontroller card.

ASCII characters are used to transfer data between PC and microcontroller

You can use a terminal emulator on the PC, there is no special program for the PC

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Sample Program

The project worksheet contains a sample program

This is the same program used to test the serial port of your microcontroller card in the lab

Action - every second, the microcontroller sends the time to the PC as a text string over the serial interface .

The time can be displayed on a PC using any terminal program (9600bps, 8 bit, no parity)

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First Task

You first job is to understand the program and produce documentation for it.

To do this you should:

o Compile and run the program

o Add comments to the program

o Produce Pseudocode for the program

Copies of the commented program and Pseudocode must be submitted to your Supervisor

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Compiling the Program

The C program on the worksheet is to run on the microcontroller.

This processor uses different machine instructions to the PC

Visual C++ produces machine instructions for the PC - it won’t run on the microcontroller.

CC51 is a C compiler which produces machine instructions which run on the microcontroller

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The Process of Compiling

To compile a program for the microcontroller:Produce the text C code using any text editorUse CC51 to compile the program

o Make sure there are no errors

Transfer the file produced into the microcontroller (use EPROM programmer)o Compiler produces a HEX format file

Insert the microcontroller in your card and test.

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Documenting the Program

Before starting to write a new program, you will gain some practice at documenting programs

You should :

1. Understand what the program does(run it if necessary)

2. Add comments to the program

3. Write a Pseudocode description of the program(this should be done before writing a program)

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Sample Documentation

Consider the program on the microcontroller used with the dice as an example.

Problem :

Send a ‘Y’ when the button is pressed and send a ‘N’ when the button is released. At the same time, display any received character on the LEDs.

The following shows 3 ways to describe the problem.

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State Diagram

Key Released Key Pressed

Press

Releasechar

received

charreceived

DisplayPattern

DisplayPattern

action trigger

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Flow ChartStart

Is keypressed

Is charreceived

Get char

Display Pattern

Send 'Y'

Is keyreleased

Is charreceived

Get char

Display Pattern

Yes Yes

No No

Yes

Yes

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Pseudo CodeDo forever [while ( true is true )]{ while ( key not pressed )

{ if (character received){ get character

display pattern }}

send ‘Y’while ( key pressed )

{if (character received){ get character

display pattern }}

send ‘N’}

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Comments on TechniquesState Diagram – good graphical technique for

describing a process. Doesn’t help much in writing program. Can be used to clarify design before writing pseudocode

Flow Chart – good at describing sequential processes. Doesn’t help much in writing high level programs, but good for machine level coding.

Pseudocode – good at describing complex processes. Helps to write high level code.

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Creating a Stop Watch Function

You now understand the program ! ! !You must modify the program to make it work

as a stop watch.Stop watch control is via the serial interfaceCharacters entered on the PC keyboard will

control the Stop watch<space> hitting the space bar will toggle

the Stop watch on and offR resets the display to zero

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System Diagram

Type <space> to turn on

Type <space> to turn off

Send ASCII characters of time to display

00:01:45

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What You Must DoFirstly, make sure you understand what the

Stop watch does – ask if you don’t understand

Modify the Pseudocode for the clock program to make it act as a stop watch

Code this in CProduce a text file of the programCompile using CC51Load the code into the microcontrollerTest the functionality and debug if necessary

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Creating a Clock Function

Create a new Pseudocode for a Clock which responds to the following commands :

A sets the clock to adjust mode. In adjust mode the clock stops until it receives <CR>

Digit in adjust mode, the digits are entered into

1021 the current time

<BS> in adjust mode, go back to last entered digit

<CR> in adjust mode, returns to clock mode

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What You Must Do

Again, you must first understand the problem.In this example, the functionality isn’t so well

defined – you have some options, e.g.o What is displayed on the PC in adjust mode

o What is displayed on PC when a <BS> is received

When you have decided, write Pseudocodeo A State Diagram may help planning

Produce the C program, compile, test and debug

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Integrating the Functions

When both Stop watch and Clock are working :Try to combine both Stop watch and Clock into 1

program.The combined program should respond to the

extra commands :

C if in Stop watch mode, switch to Clock mode

S if in Clock mode, switch to Stop watch mode

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The Combined Clock

The Clock must keep the right time, even if it is in Stop watch mode.

Hence, clock must keep running in both modesThe program will need a separate variables for

the Clock and Stop watch.The Stop Watch can keep running in Clock modeThe Clock will stop in adjust mode – you can

decide what the Stop watch does.

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Working with the Push Button

So far, all control has been using the PC keyboard sending ASCII characters to the microcontroller.

Here, go back to the Stop watch to make it controlled by the button on the card

Control is :

Push buttontoggles the stop watch on and off

Hold button if pushed >1sec, time resets to zero

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What you must submit

For all 4 programs, you must submit a short report on your program containing:

o The Pseudocode

o The C program (including comments)

o A description of the operation of the program

Submit report when all 4 programs are done.

Your supervisor will check to see your program working before moving to the next stage.

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For the Brighter Students

It is possible that some groups will finish the three programs within 4 weeks.

We do not expect all groups to finish that quickly. However, you must finish all three programs.

The faster groups can then move on the next project task – implementing a network.

This task has scope for groups to make their own design.

Documents

Task 2 Briefing